The present invention relates to automotive vehicle brake lathes configured for resurfacing brake rotor components, and in particular, to an improved on-car brake lathe apparatus and a method for compensating for runout between an on-car brake lathe and a vehicle wheel hub to which the on-car brake lathe is secured for a brake rotor resurfacing operation.
One of the main components of a vehicle wheel braking system employing rotor brakes are the brake rotors, which provide a solid rotating surface against which the stationary brake friction pads are clamped or compressed to generate a frictional force, slowing the rotational movement of the brake rotors and the associated vehicle wheels. The brake rotors are subjected to repeated and substantial frictional forces by the brake friction pads, and over time, become worn. Uneven application of braking force, debris, or uneven frictional surfaces on the brake friction pads can result in the formation of grooves, channels, or scratches in the surfaces of the brake rotors. Repeated heating and cooling of the brake rotor resulting in extreme temperature variations can additionally result in the lateral warping of the brake rotor.
A worn or warped brake rotor may be resurfaced by cutting or grinding to provide a uniform smooth brake friction pad contact surface if sufficient brake rotor material remains to provide an adequate braking surface without compromising the structural integrity of the vehicle braking system. However, once a brake rotor has been worn below a minimum safe thickness, it is unable to safely dissipate the heat generated by a brake application, and must be replaced.
To provide for a uniform surface, any abnormalities in the brake rotor, such as a lateral warping must be detected and removed during the resurfacing procedures. An additional source of lateral warping defects in a brake rotor or brake rotor is often over tightened attachment bolts or an uneven mounting surface onto which the brake rotor is secured in the vehicle wheel assembly. If the brake rotor is removed from the vehicle wheel assembly for a resurfacing operation on a fixed or “bench” brake lathe any abnormalities or defects resulting from the mounting of the brake rotor to the vehicle wheel assembly may not be accurately identified or corrected during the resurfacing procedure. Accordingly, a variety of brake resurfacing machines or brake lathes have been developed to resurface brake rotors while they remain mounted to the vehicle wheel assembly.
Brake resurfacing machines or brake lathes configured to resurface brake rotors mounted to a vehicle wheel assembly are commonly referred to as on-car brake lathes. Examples of an on-car brake lathe include the OCL-360 and OCL-400 brake lathes sold by Hunter Engineering Co. of Bridgeton, Mo. By eliminating the need to remove the brake rotor from the vehicle wheel assembly, the overall efficiency of the resurfacing procedure is improved, and the chances for operator induced error are reduced. However, the resurfacing of brake rotors which remain mounted to the vehicle wheel assembly requires that the on-car brake lathe and the vehicle wheel assembly, including the brake rotor, be aligned along a common axis, typically, the rotational axis of the vehicle wheel assembly hub onto which the on-car brake lathe is secured.
Often, the hub surface to which the vehicle wheel assembly mounts is not aligned within a required tolerance to the axis of rotation for the axle upon which the vehicle wheel assembly is secured. This deviation between the hub surface and the axis of rotation for the wheel assembly is referred to as lateral runout, and must be compensated for either manually or automatically before beginning the resurfacing procedures with the on-car brake lathe.
Manual runout compensation procedures are tedious and complex. First, an operator secures the output spindle of the on-car brake lathe to the vehicle wheel hub using a suitable adapter. Next, a motor in the on-car brake lathe is activated to rotate the output spindle, the adapter, and brake rotor. Any runout present in the system is directly measured by one or more measurement devices, which provide the operator with a suitable visual indication representative of the actual runout experienced by the on-car brake lathe as the adapter is rotated through one or more complete rotations. Using the visual indication, the operator manually adjusts one or more mechanical adjustment elements, such as screws or dials, altering the rotational axis of the on-car brake lathe output spindle to reduce the observed runout to within an acceptable tolerance for performing the resurfacing of the brake rotor.
To reduce the observed runout to within the desired tolerances using the manual runout compensation procedure usually requires several iterations when carried out by a skilled operator. The extra time spent by an operator to setup the on-car brake lathe and perform the manual runout compensation can substantially increase the time required to complete a brake rotor resurfacing, resulting in a corresponding increase in cost and lost productivity.
Accordingly, a number of on-car brake lathe devices have been configured with active automatic runout compensation mechanisms which do not require significant operator input. Such active automatic runout compensation mechanisms are shown in European Patent Application No. 1 0172 343 A1 to Costruzioni Mechaniche Caorle S.p.A., based on Italian Patent No. 0248591 Y1, and in U.S. Pat. No. 6,101,911 to Newell et al. The automatic runout compensation mechanism shown in the '911 Newell et al. patent includes at least one adjustment rotor interposed between a pair of adapters and which is concentric about an axial drive shaft. The on-car brake lathe motor and cutting elements are secured to one adapter, and the entire mechanism secured to the vehicle wheel hub via the second adapter. The adjustment rotor includes a slanted surface in engagement with either a second adjustment rotor having an opposing slanted surface or one of the adapters. An adjustment mechanism is utilized to alter the rotational orientation of the adjustment rotor about the axis of the axial drive shaft.
As the components of the '911 Newell et al. automatic runout compensation mechanism are rotated about the axis at a fixed speed of 120 PRM, runout is detected by an accelerometer. A processor receives an output signal from the accelerometer and provides corresponding control signals to an adjustment mechanism. Alteration of the rotation position of the adjustment rotor about the axis of the axial drive shaft as the components are rotated at the relatively high fixed rotational speed of 120 RPM compensates for the detected runout by attempting to alter the angle at which the two slanted surfaces are engaged, and correspondingly the angle between the first and second adapters. Due to significant high speed vibrations and the interaction of the various rotating components, such as bearings, gears, and shaft, errors are induced in the automatic runout compensation sensor signals. Thus, automatic runout compensation typically requires several complete rotations of the various components about the axis before the adjustment rotor rotational position is sufficiently altered to compensate for any detected runout.
The automated adjustment mechanism of the '911 Newell et al. patent associated with the use of the one or more slant rotors is a costly and complex mechanical arrangement. The mechanism requires an initial phasing or alignment of the adjustment rotors, followed by a lengthy trial-and-error adjustment process to compensate for any detected runout.
Accordingly, there is a need for on-car brake lathes having improved precision runout compensation mechanisms, which are not subjected to rotational movement noise and vibrations during runout measurements, and which can quickly and accurately compensate for detected runout, but which do not require complex and costly components.
With conventional on-car brake lathes, it is necessary to invert the orientation of the lathe when switching between sides of a vehicle. Inverting the lathe inverts the operator control panel, and can render the operation of the controls difficult, particularly as the number of controls or displays increased. Accordingly, there is a further need for an on-car brake lathe having a control panel which is adjustable so as to be presentable to an operator at a selected orientation, independent of the orientation of the on-car brake lathe.
Traditionally, on-car and bench brake lathes utilize motors or drive systems configured for operation at a fixed spindle RPM and feed rate. During rotor cutting or resurfacing, a resonance or vibration, commonly referred to as “chatter”, can develop between the rotor cutting tools and the rotor surface, resulting at best in an uneven resurfacing of the brake rotor, or at worst, in severe damage to the rotor surface or rotor cutting tools themselves. Accordingly, the fixed spindle RPM and feed rates in traditional on-car and bench brake lathes are selected to be below the rates at which the resonance or vibration is likely to occur. Alternatively, such as shown in U.S. Pat. No. 6,591,720 B1 to Greenwald et al., vibration damping or attenuating components such as pads or elastomeric bands are brought into contact with the brake rotor during resurfacing to control or reduce undesired “chatter” resonance or vibrations.
Since it is known that “chatter” vibrations or resonances are a function of the spindle RPM, feed rates, and depth of the resurfacing cut, it would be advantageous to provide on-car and bench brake lathes with a reliable system to detect the presence of “chatter” vibrations or resonance during the cutting of the rotor, and to configure the brake lathes with one or more automatic adjustments to reduce or eliminate the vibrations before it affects the quality of the surface finish on the rotor. Since the rates at which the resonance or vibration are likely to occur vary for brake rotors of different sizes, thicknesses, and materials, it would be advantageous to provide an on-car brake lathe which is capable of varying the spindle RPM during the resurfacing of a brake rotor and, optionally, the linear feed rate of the cutting implements, up to a maximum rate at which a desired brake rotor resurfacing quality can be achieved, thereby reducing operator time require to resurface a brake rotor.
It is desirable to create a brake resurfacing system that will sense when the cut is completed and automatically stop the operation of the brake lathe, thereby reducing the time required for the operator to prepare the brake lathe to cut the next rotor.
Some vehicles are equipped with locking differentials in the vehicle drive train that engage when a difference in wheel rotational speed from one side of the vehicle to the other reaches approximately 100 RPM. When the locking mechanism engages, as may occur during rotation of a brake rotor by an on-car brake lathe, the resulting change in rotational resistance can violently rotate the entire on-car lathe body. It is desirable to provide an on-car brake lathe with safety features configured to automatically stop the lathe rotation if a sudden resistance is encountered in the cut.
With a wide variety of information related to vehicle specifications, including brake rotor thicknesses and dimensions, it would be advantageous to provide a brake lathe system with a communications interface by which the lathe can acquire at least vehicle specifications from a data network or other automotive service device. It is also desired that this communication system would be able to send data to a remote printer or console.
U.S. Pat. No. 6,363,821 B1 to Greenwald et al. discloses a vehicle brake lathe incorporating cutting tip contact sensors to provide signals to a controlling microprocessor to facilitate automated movement of the cutting tips relative to a brake rotor surface, as well as a determination of a depth of cut. However, the '821 Greenwald et al. patent does not appear to provide the brake lathe operator with a simple and efficient indication of contact between each individual cutting tip and the brake rotor surface. Accordingly, there is a need to provide improved feedback from an operating brake lathe to an operator, permitting proper adjustments of the cutting tips for depth of cut and runout measurement during rotor resurfacing, and ensuring proper engagement between a visually occluded cutting tip and a brake rotor surface without requiring an operator to move to within close proximity of rotating components during an adjustment or resurfacing procedure.
In addition to identifying contact between the cutting tips and a brake rotor surface, it is useful to provide a displayed measure of a depth of cut provided by the cutting tips. U.S. Pat. No. 6,363,821 B1 to Greenwald et al. provides a displayed depth of cut utilizing a displacement gauge positioned relative to each tool holder on a brake lathe. The displacement gauge in the '821 Greenwald, et al. patent directly measures the spatial separation or displacement between the two tool holders. To obtain a depth of cut measurement, an initial separation distance between the cutting bits is compared with a subsequent separation distance after a depth of cut adjustment has been made to a cutting bit. The calculated change in separation distance corresponds to the change in depth of cut of the cutting bit from the initial position plus the depth of cut for the opposite cutting bit (which is zero if it has not yet been adjusted). Hence, the position of both tool holders must be monitored to provide a depth of cut measurement for a single tool holder. Accordingly, it would be advantageous to provide a simplified depth-of-cut measurement system for a single tool holder on a brake lathe which does not require information related to the position of a second tool holder, or a measurement of displacement between a pair of tool holders, to provide a depth of cut measurement.